Oxytalan fibres in the periodontal ligament of equine molar cheek teeth

The distribution and arrangement of oxytalan fibres were examined in periodontal specimens of cheek teeth from seven horses. Oxidation prior to aldehyde fuchsin exposition permitted a selective staining of the oxytalan fibres, which are a distinct component of the elastic fibre system. On three horizontal levels of the periodontium--(a) subgingival, (b) middle third and (c) apical--two oxytalan fibre groups were shown histologically: 'blood vessel-related' and 'independent' oxytalan fibres. In levels a and b, both groups were arranged in a typical occluso-apical alignment along the reserve crown. Single oxytalan fibres deviated from their general course in order to attach to the cementum. In these cemental entheses the oxytalan fibres ran parallel to collagen fibre bundles. The interpretation of such morphological features emphasized the oxytalan fibres' capacity to improve the stability of periodontal blood vessel walls during masticatory movements. Level c, especially in regions next to the persisting epithelial root sheath, is the site of oxytalan fibre generation. This is a prerequisite for the facilitation of periodontal regeneration and reorganization during dental growth and eruption.     

Collagen fiber architecture of the periodontal ligament in equine cheek teeth

The objective of this study was to examine the spatial arrangement of the fiber apparatus of the equine periodontium which is supposed to meet two contrary requirements: (1) to attach the tooth firmly and elastically to the alveolar bone; and, to be appropriately remodeled and reconstructed in order to facilitate the prolonged eruption of the tooth. Specimens of periodontal ligament were obtained from the buccal and lingual/palatal aspects of the first molars from the maxilla and mandible of 12 horses. The animals were assigned to three age groups. Histological sections were prepared from three specific horizontal levels of the periodontal ligament and examined with conventional and polarized-light microscopy. At the gingival level, collagen fascicles (diameter > 200 microm) were densely packed. Their spatial alignment was the same in all age groups. The architecture of the collagen fiber apparatus differed at the middle and apical levels in the three age groups. There was a clear distinction between fibers, bundles, and fascicles. Bundling of collagen fibers, density of the fiber arrangement, and collagen fascicles with an alveolo-cemental orientation increased with age. The collagen fiber apparatus of the equine periodontal ligament is highly adaptive, responding continuously to the dynamic changes in the periodontal environment. Site-specific arrangements and age-dependent structural variations are assumed to maintain tooth support as the reserve crown gradually decreases in length with progressive dental attrition. Most of the age-dependent changes to the periodontal ligament in teeth examined in this study occurred at the apical level. The apical region of young teeth had no periodontal attachment, while the roots of older teeth were firmly attached to the alveolus. When evaluating periodontal ligament development, the individual tooth's 'dental age' should be considered rather than the animal's age to account for individual tooth eruption times.     

Finite element analysis in 3-D models of equine cheek teeth

Periodontal diseases occur frequently in equine dentistry and excessive strain in biological tissues is assumed to be a predisposing factor in their development. Finite element (FE) analysis enables strains and stresses occurring in the periodontium to be calculated and is a useful tool for testing this hypothesis. The current study aimed to establish reliable 3-D models from equine maxillary and mandibular cheek teeth for use in FE simulations, with particular attention to the detailed construction of the periodontal ligament (PDL). Age-related morphological aspects of the teeth and the periodontium were also considered by constructing different models for three defined age groups. Finally, the biomechanical behaviour of the equine PDL was examined during experimental tooth intrusion (i.e. axial displacement of the tooth into its alveolar socket). The results showed an increase in intrusion with increasing age due to age-related changes in the periodontal elastic properties. The general stress level in PDL and surrounding bone also increased with age. Reliable FE models were established to calculate aetiologically relevant biomechanical effects occurring in the equine periodontium.     

Immunohistochemical identification of lymphatic vessels in the periodontium of equine cheek teeth

Immunohistochemical detection of lymphatic capillaries was performed in the periodontium of maxillary and mandibular cheek teeth from 6 horses (aged 3-23 years). Tissue sections of the periodontium were taken at 4 different horizontal levels along the long axis of the tooth. The specimens were processed for immunoreaction with anti-Prox1, in order to distinguish lymphatic endothelium from blood vascular endothelium. Lymphatic vessels were detected in all periodontal tissues except for the dental cementum. Lymphatic capillaries were most densely distributed in the gingiva compared to other tissues of the periodontium. Lymphatic capillaries were found most consistently in samples taken from the gingival and subgingival regions in all horses examined. Within these levels, the gingiva as well as the spongiosa of the maxillary and mandibular bone had the greatest incidence of lymphatic vessels. Considering the distinct distribution of the lymphatic capillaries in the periodontium of the maxillary and mandibular cheek teeth, two complementary lymphatic drainage pathways are proposed: (1) superficial lymph drainage via the gingiva, emptying into the mandibular lymph nodes; (2) deep lymph drainage via the mandibular and maxillary spongiosa, emptying into the mandibular and retropharyngeal lymph nodes, respectively.     

A study of sub-occlusal secondary dentine thickness in overgrown equine cheek teeth

The presence of cheek tooth loss or defects, with subsequent overgrowth of the opposing teeth, is common in horses. Little is known about the factors that control the deposition of sub-occlusal secondary dentine (SO2D) in normal equine teeth, but these are likely to include stimulation of the occlusal surface. There appears to be no information on the possible alterations to this process when teeth develop overgrowths and, consequently, of the net effect on SO2D thickness caused by reduced stimulation of the occlusal surface and of absent/reduced normal occlusal wear (attrition). Knowledge of the likely thickness of SO2D in overgrown teeth may help reduce the risks of pulp horn exposure or thermal damage during therapeutic reduction of overgrowths. This study utilised 24 permanent cheek teeth (CT) with overgrowths (mean overgrowth height: 9.5 mm; range, 3.4-17.9 mm), and 18 control CT obtained from 15 horses of different breeds and ages. The thickness of SO2D was measured above 94 matched pulp horns in control and overgrown CT and showed a mean value of 12.14 mm (range 1.87-36.02 mm) in overgrown teeth and of 10.25 mm (range 2.64-17.26 mm) in controls. There was no significant difference between SO2D thickness in overgrown (mean 11.38 mm) and control (11.41 mm) mandibular CT, but SO2D was significantly thicker in overgrown (mean 12.57 mm) as compared to control maxillary (9.41 mm) CT. A comparison of SO2D thickness above the 94 matched pulp horns in overgrown and control teeth showed that 49% (46/94) of pulps in overgrown teeth had less SO2D overlying them than had control teeth. Of major clinical relevance was that the height of dental overgrowths was greater than SO2D thickness over one or more pulp horns in 14/24 overgrown teeth. Consequently, reduction of these overgrown teeth to the level of adjacent normal-height teeth would cause occlusal pulp exposure in 58% of teeth, in addition to possible thermal damage to additional pulp horns. It was concluded that equine CT overgrowths should be gradually reduced, by a few millimetres at a time, over a prolonged period.     

Pathological studies of cheek teeth apical infections in the horse: 2. Quantitative measurements in normal equine dentine

Measurements of primary, regular and irregular secondary dentine and pulp dimensions were made on transverse, sub-occlusal and mid-tooth sections, of 40 maxillary and 42 mandibular control equine cheek teeth (CT) of different ages. Maxillary and mandibular CT primary dentine in different age groups had a mean thickness of 922–1065 μm and 1099–1179 μm, respectively, on the lateral aspects, and 1574–2035 μm and 1155–1330 μm, respectively, on the medial aspects of pulp horns. Surprisingly, some increase in thickness was found in some mandibular CT primary enamel in the first few years following eruption.Regular secondary dentine thickness increased with age, for example at mid-tooth level in mandibular CT from 124 μm at 3 years dental age to 290 μm at >7 years dental age on the lateral aspect of pulp horns, and from 166 μm to 509 μm on the medial aspects of pulp horns, indicating a deposition rate of 0.5–10 μm/day. This type of dentine was thicker sub-occlusally than in the mid-tooth region. Maxillary dentinal dimensions showed a similar age-related increase in thickness. Maxillary CT dentine was significantly thicker (72% in primary, 43% in regular secondary dentine) on the medial compared to the lateral aspects of pulp horns, but mandibular CT dentine was just 15% and 14% thicker in primary and regular secondary dentine thickness, respectively, on the their medial as compared to their lateral aspects. Dentinal and pulp dimensions varied between individual pulp horns, Triadan tooth position, and dental age, with complex interactions between these variables for some parameters.     

Pathological studies of cheek teeth apical infections in the horse. 1: Normal endodontic anatomy and dentinal structure of equine cheek teeth

Morphological examinations were performed on 100 normal equine cheek teeth (CT) of 1–12 years dental age (i.e. time since eruption), using gross examination, dissection microscopy, computerised axial tomography, and decalcified and undecalcified histology. The CT in Triadan 07–10 positions consistently had five pulp horns, but the 06 CT had an additional pulp horn more rostrally. Mandibular and maxillary Triadan 11s had six and seven pulp horns, respectively. Sections of CT taken 2–6 mm below the occlusal surface (variation due to normal undulating occlusal surface) showed the presence of pulp in up to 50% of individual maxillary CT pulp horns, and in up to 25% of individual mandibular CT pulp horns. The histological appearances of primary and secondary dentine were described and it is proposed that the type of dentine present most centrally in every pulp chamber examined, currently termed tertiary dentine, should be re-classified as irregular secondary dentine, and that the term tertiary dentine be reserved for the focal areas of dentine laid down following insult to dentine or pulp.     

The use of radiography for diagnosis of apical infection of equine cheek teeth

Despite recent developments in advanced imaging, radiography remains the most commonly employed imaging modality for investigating apical infection of cheek teeth in horses. Radiographic technique, knowledge of the normal anatomy and horse compliance are paramount for acquiring good quality dental radiographs. Interpretation of subtle pathology can be difficult for even the most experienced radiologist; however, in more chronic cases, identification of dental abnormalities is easier.     

Prevalence of occlusal pulpar exposure in 110 equine cheek teeth with apical infections and idiopathic fractures

Examination of 110 cheek teeth (CT) that were clinically extracted (between 2004 and 2008) because of apical infection (n = 79; mean dental age 3.5 years) or idiopathic CT fractures (n = 31; median dental age 8.5 years), including examinations of transverse and longitudinal sections, showed the apical infections to be mainly (68%) due to anachoresis, with the residual cases caused by periodontal spread, infundibular caries spread, fissure fractures and dysplasia.The idiopathic fracture patterns were similar to previously described patterns. Occlusal pulpar exposure was found in 32% of apically infected CT, including multiple pulps in 27% and a single pulp in 5%. However, 10% of apically infected CT had changes to the occlusal secondary dentine, termed occlusal pitting, but did not have exposure of the underlying pulp. Multiple pulpar exposures occurred in some CT with apical infections, and the combination of pulp involvement reflects the anatomical relationships of these pulps. A higher proportion (42%) of CT extracted because idiopathic fractures had pulpar exposure (26% multiple, 16% single pulps), especially with midline sagittal maxillary and miscellaneous pattern mandibular CT fractures, but only (3%) had occlusal pitting.     

Description of a technique for orthograde endodontic treatment of equine cheek teeth with apical infections

An orthograde endodontic method, similar to that used in human dentistry, is described for use on endodontically diseased permanent cheek teeth in horses. The technique has been adapted to meet the anatomical and physiological differences between hypsodont and brachyodont teeth and is performed in sedated horses. The techniques of debriding the pulp cavity and use of dental materials which fulfil the requirements for equine teeth are presented here. The results of this technique appear to be promising but have yet to be evaluated in a peer‐reviewed study. By using orthograde endodontic therapy on sedated horses it is now possible to save endodontically diseased permanent cheek teeth.     

Occlusal angles of cheek teeth in normal horses and horses with dental disease

The angle between the occlusal surface of the tooth and the horizontal plane of 687 cheek teeth from the skulls of 22 horses without gross dental disorders and 11 horses with dental disorders were measured by using stiff malleable wire as an imprint. Each measurement was repeated five times and the mean angle was recorded. In the normal skulls, the mean occlusal angles of the mandibular cheek teeth ranged from 19.2 degrees at the Triadan 06 position to 30 degrees at the 11 position, and these angles were significantly greater than the occlusal angles of the opposing maxillary cheek teeth (range 12.5 degrees to 18 degrees) at all the positions except the 06. The rostral mandibular cheek teeth had significantly lower occlusal angles than the caudal mandibular cheek teeth, but the converse was true for the maxillary teeth. In the skulls with dental disorders the occlusal angles of the mandibular cheek teeth ranged from 15.6 degrees to 28.5 degrees , and of the maxillary cheek teeth from 9.2 degrees to 16.4 degrees. They were not significantly different from the angles of the teeth from the normal skulls, except at the 06 position, where they were smaller.